Child & Teen BMI Percentile Calculator
Find your child's BMI-for-age percentile using the CDC growth charts (ages 2–19). Get their weight-status category and the healthy BMI range for their age and sex.
For children and teens, BMI is calculated exactly like an adult’s — weight ÷ height² — but the number is read against age- and sex-specific growth charts rather than fixed cut-offs. That’s because a healthy BMI for a 6-year-old is very different from a healthy BMI for a 16-year-old, and it differs between boys and girls. Enter height and weight in metric (kg, cm) or imperial (lb, in) units — the calculator converts automatically.
How the percentile works
This calculator uses the CDC 2000 BMI-for-age growth charts (the LMS reference method) to convert your child’s BMI into a percentile for their exact age in months and their sex. A result at the 70th percentile means the child’s BMI is higher than 70% of children the same age and sex in the reference population.
The CDC weight-status categories
| Category | BMI-for-age percentile |
|---|---|
| Underweight | Below the 5th percentile |
| Healthy weight | 5th to below the 85th percentile |
| Overweight | 85th to below the 95th percentile |
| Obese | At or above the 95th percentile |
| Severe obesity | At or above 120% of the 95th percentile (or a BMI of 35+) |
The tool also shows the healthy BMI range for your child’s age (the 5th–85th percentile band) and the median (50th-percentile) BMI, so you can see where they sit relative to typical growth.
Percent of the 95th percentile
Very high BMIs all crowd together near the 99th percentile, so the percentile alone can’t tell apart a child who is somewhat above the obesity line from one who is far above it. To fix that, the calculator also reports the child’s BMI as a percent of the 95th-percentile BMI for their age — the metric the CDC now uses to define severe obesity (120% of the 95th percentile or higher).
Ages 2 to 19
BMI-for-age applies from 2 through 19 years. For children under 2, growth is tracked with the WHO weight-for-length charts instead, so this calculator is limited to age 2 and above. From age 20, the fixed adult thresholds take over — switch to the standard BMI calculator for anyone in that range.
A screening tool, not a diagnosis
BMI percentile is a helpful screen, but it doesn’t measure body fat directly and can’t account for a very muscular build or a growth spurt. Read it as one data point. A pediatrician can interpret the trend over time alongside your child’s overall health — that context matters far more than any single reading.
Frequently asked questions
How do you calculate a child's BMI?
The same way as an adult's: divide weight by height squared. In metric units that's weight in kilograms ÷ height in metres squared — for a child of 30 kg and 1.35 m, BMI = 30 ÷ 1.35² ≈ 16.5. In imperial units, multiply weight in pounds by 703 and divide by height in inches squared — 66 lb and 53 in gives 703 × 66 ÷ 53² ≈ 16.5. This calculator works with either unit system and converts automatically. The raw number is then looked up on the CDC BMI-for-age chart for the child's exact age and sex to get a percentile.
Why is children's BMI calculated differently from adults'?
The BMI number is worked out the same way — weight divided by height squared — but it's interpreted differently. Children's body fat changes constantly as they grow and differs between boys and girls, so a raw BMI means little on its own. Instead it's compared with the CDC growth charts to give a percentile for the child's exact age and sex.
What is a BMI percentile?
The percentile shows how your child's BMI compares with other children of the same age and sex. A BMI in the 60th percentile means the child's BMI is higher than 60% of that reference group. The CDC weight-status bands are: underweight below the 5th percentile, healthy weight 5th to below 85th, overweight 85th to below 95th, and obese at or above the 95th percentile.
What ages does this calculator cover?
It covers children and teens from 2 to 19 years, matching the CDC BMI-for-age growth charts. For babies and toddlers under 2, clinicians use the WHO weight-for-length charts instead, so this tool doesn't apply below age 2.
My child's BMI percentile is high — what should I do?
A single reading is a screening result, not a diagnosis. Growth naturally varies, and a percentile can shift with a growth spurt. Talk to your pediatrician, who can look at the trend over time, family history, and overall health before drawing any conclusion.
References
- Centers for Disease Control and Prevention — BMI-for-age growth charts and percentile data
- Kuczmarski RJ, et al. 2000 CDC Growth Charts for the United States: methods and development. Vital Health Stat 11. 2002
- Centers for Disease Control and Prevention — About Child & Teen BMI
- AAP / HealthyChildren.org - Body Mass Index formula for children